In certain situations, it may be required to obtain a historical record of drug use. Urine and saliva detection rates are restricted to the metabolic half life of drugs while in the body. Quitting before a drug test can therefore cause a negative result when in fact the individual has a history of drug abuse. Institutions or employers may want to know this information. All that is required for testing is several strains of hair. The existence of drugs in the hair is based on a simple principle. Drugs are ingested into the body then flow into a person's bloodstream which feeds developing hair follicles. Therefore, small amounts of the target drug or drug metabolite collect in the hair follicle and become trapped in the center of the hair shaft as it grows out from the hair follicle. Average growth rates for human hair are roughly one-half inch per month. By testing for the drugs at different points in the hair shaft center on a piece of hair, a rather precise approximation can then be made as to how long a particular drug has been used. Target drug or drug metabolites cannot be washed, bleached or flushed out of the hair structure because the residue is chemically and structurally stable for a long period of time. Also there is no chance of sample contamination or manipulation. A gas chromatography/mass spectrometry (GC/MS) laboratory analysis of the hair is required to accurately provide the historical use record. Generally it takes about 5 days for drugs to show up in a person's hair and will be detectable in new hair growth for up to 90 days.
The Gas Chromatography is used to break up molecules that are then analyzed by the Mass Spectrometer. A solution is added to the specimen from the subject in question that converts drug metabolites into a form that is reactive to Gas Chromatography. The specimen is heated to change it to gas and the gas is collected in columns that isolate drug metabolites found in the specimen. The gas samples are collected at precise intervals, (the conversion rate from solid to gas being known) and moved to the Mass Spectrometer.
The collected specimen is hit with a barrage of electrons creating a cation, ionization then accelerated by an electrical field and strained through a receptor that only allows certain particles to pass through. This is then forced through a magnetic field that has a controlled strength. The specimen and the field are oppositely charged creating a deflection of the particles that are then forced through another receptor and into a collector. The operator controls the electrical and magnetic fields so that the mass of the cation is promptly verified. Every compound has a specific weight and charge and can be identified by these properties. It is very easy then to determine the presence of drug metabolites and confirm drug abuse by the subject.
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